The present invention relates to an optical head, and more particularly to an integrated optical head which is small in size and can access information at high speed.
An integrated optical head is proposed in a Japanese patent application No. JP-A-60-129,938. In this optical head, reflected light from an optical disk is received by a curved grating which is formed in an optical waveguide, and then led to a photodetector to detect a focal error signal and a tracking signal by the photodetector. The above-identified patent application, however, does not disclose an actuator for locating a light spot at an optimum position on the basis of the focal error signal and tracking signal.
Another optical head is disclosed in a Japanese patent application No. JP-A-61-61,246. In this optical head, a light beam from a laser device is shaped by a grating which is formed on an optical guide, and then led to a curved grating, light emerging from the curved grating is focused on an optical disk, and reflected light from the optical disk is detected by a photosensor. In this optical head, however, a conventional force motor coil is used as an actuator for performing a focus control operation and a tracking control operation on the basis of an output signal from the photosensor. Accordingly, it is impossible to access information at high speed, and moreover the shape and size of the optical head are affected greatly by those of the above actuator.
An optical disk is tens of times greater in recording density than a magnetic disk, and has a long life because there is no contact with the optical recording medium. However, a conventional optical head is large in size and slow in response speed. Further, in order to increase the recording capacity of an optical disk apparatus, it is necessary for an optical head to access multiple disks. Accordingly, it is desirable that the optical head is small in thickness.
In the optical head disclosed in the latter patent application, no regard is paid to quick access to information and the access of the optical head to a multiplicity of optical disks. That is, the optical head responds slowly to a focus control device, and moreover is large in size. Thus, it is required to make the distance between adjacent optical disks large, thereby increasing the size of an optical file apparatus. Further, since the above optical head is an integrated optical head, optical elements included in the optical head are low in working efficiency. Accordingly, the intensity of light incident on a photosensor is weak, and thus it is difficult to produce a reliable focus control.